Electric switch



, y 1943- M. N. RUSSELL z-rrm. 2,318,015

ELECTRIC SWITCH Filed March 30, 1940 2 Sheets-Sheet l May 4, 1943.

M. N. RUSSELL ETAL 2,318,015

ELECTRIC SWITCH Filed March 30, 1940 2 Sheets-Sheet 2 gwue/wtom" 15. WWW 7 W M 9 M Mb! Patented May 4, 1943 UNITED STATES PATENT, OFFICE ELECTRIC SWITCH Mark N. Russell and Saul Keilien, Syracuse, N. Y., assignors to Pass & Seymour, Inc., Syracuse, N. Y., a corporation of New York Application March 30, 194?, Serial No. 327,002

8 Claims.

This invention relates to electric circuit makers and breakers and more particularly to small electric switches of the snap type primarily intended for operation with loads which are materially abovenormal at the instant of closing of the circuit whereby the switch contacts are unduly loaded and subjected to the possibility of destructive arcing during the brief interval occupied by the closing of the contacts.

Heretofore in most prior art constructions of air-break switches, two major considerations have led to the type of design now prevalent. The first of these and perhaps also foremost in the mind of the manufacturer, is the ability to carry the rated current under conventional operating conditions and to handle reasonable overloads for brief periods. Secondly, great efforts have been expended in the design of such switches to avoid the destructive action of arcs drawn when the circuit is broken. This applies equally to switches intended for direct and alternating current.

Since the examination of a partly or wholly destroyed switch always discloses burning of both the stationary and movable contacts on the portions which last separate, and usually first engage, many switches have been designed with supplementary arcing contacts which separate after the main contacts have been opened and which may be of highly refractory material, although probably not so suitable, by reason of high resistance, for constant operation, which is therefore taken care of by the main contacts.

In the smaller switches, such as wall type snap switches of the pushbutton or toggle lever type, the tendency has been, because of the limited space available-to attempt to solve the problem by rapidity of movement of the contacts, endeavoring to separate them with such speed as to materially shorten the period of arcing. In some cases arc-quenching or sn-uifing devices of one sort or another have been resorted to.

It has recently been recognized that the major damage to wall type switches and others used with tungsten filament lamp loads is occasioned on the making of the circuit rather than on the breaking thereof because of a, peculiar property of the tungsten used in the filaments of the. lamps. This material has a high temperature co-eflicient of resistance, i. e. its resistance is very much lower when cold than when heated to incandescence. Thus the current flow to such lamps when cold may vary from eight to ten times the normal current flow when they are heated, dependent to some extent on the characteristics of the circuit into which they are connected. It is easy to appreciate the detrimental efiects of such currents on switches rated for the normal operating lamp load.

The demands on snap switches of the smaller capacities from say 10 to 30 amperes have increased in recent years due principally to the higher levels of illumination now demanded, and the difilculties have been further increased by the requirement for a reduction in size of the switches, for instance so that they can be used in th interchangeable combinations with three to a single gang outlet box in some of the now more popular arrangements.

With these small sizes and heavy loads and the absence of space for arcing tips, and other supplementary aids, it is found that failures of such switches occur altogether too often and are usually due to the welding together of the contacts or their almost complete destruction by excessive pitting and burning.

The high rate of current flow to cold lamps, previously mentioned, is of extremely short duration, probably lasting only for several cycles of the usual -cycl alternating current and would probably do no serious damage if the initial electrical contact between the stationary and movable parts of the switch were perfect and so maintained until the lamps forming the load were heated to normal operating conditions. However, in the ordinary snap switches as now available, there is found to be a decided chattering of the contacts on make and before they settle down to a final position. It is unfortunate that theunstable contact condition occurs at the same time as the high current surge so that the arcs drawn between the vibrating contacts are particularly destructive.

These conditions have been considered so serious that the 1937 National Electric Code, para graph 3814, requires a switch of twice the ampere rating of the lamp load unless the switch is especially constructed for the purpose.

General purpose snap switches must operate on either alternating or direct current with a quick make and a quick break. The contacts must be brought together with a rapid snap and yet avoid single or multiple rebounds from the impact. This has been recognized heretofore and such remedies have been tried as increasing the stiffness of the switch blades or providing double contact springs of diiferent natural resonant frequencies in order to damp out vibrations. Tests, however, exhaustively conducted on the types of switches now available indicate that consistent good results are not obtained by any of these expedients and conditions such as shown in Figures 1 and 2 occur all too frequently.

It is therefore a general object of the present invention to provide a novel and improved switch mechanism in which the make" occurs with a minimum of vibration and rebound.

More particularly it is an obiect of the invention to provide in a snap switch a system of stationary and movable contacts which are adapted to be brought together at high speed without appreciable rebound or contact vibration.

It is another object of the invention to provide a pair of relatively movable contacts in which one comprises a pair of spring arms for straddle engagement over the other, said arms being of light weight and providing mutual preloading of the spring therein to prevent chattering on "make."

An important feature of the invention resides in the provision of means for preioading the springs of a pair which constitute a single contact without increasing their mass or size.

Another important feature of the invention consists in the provision of a spring arm having a contact tip for engagement with another contact by relative movement at high speed in which said spring arm is prevented from vibrating at 4 its natural resonant frequency.

A further feature of the invention consists in the provision of means for damping the action of a cantilever type spring contact without adding to the mass, size or structural complication of the same.

Other and further features and objects of the invention will be more apparent to those skilled in the art upon a consideration of the accompanying drawings and following specification wherein is disclosed a single exemplary embodiment of the invention with the understanding that such changes may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention.

In said drawings:

Figures 1 and 2 are views of two different types of snap switches particularly well illustrating the destructive effects of the modern lamp load on the light-weight movable contacts;

Figure 3 is a reproduction of an oscillogram obtained by operating an undamaged switch of the type of Figure 1;

Figure 4 is an oscillagram record of the operation of a switch of the type of Figure 2;

Figure 5 is a side elevation partly in transverse section of one type of switch constructed according to the present invention illustrtaing the snap mechanism, as well as the general arrangement of the contacts;

Figure 6 is a section on line GB of Figure 5 illustrating the approach edge of one of the stationary contacts;

Figure 7 is a side elevation on an enlarged scale of the movable contact assembly;

Figure 8 is a section on broken line 8-8 of Figure "I Figure 9 is a section on line 9-4 of Figure 7 illustrating the mutual preloading tips of the movable contact springs;

Figure 10 is a transverse section on line Iii-i0 of Figure 9; while Figures 11 and 12 are reproductions of oscillograms obtained by operating a switch of the type shown in Figures 5-10 inclusive.

As a prelude to developing a satisfactory construction for the contacts of a small-size, high of a number of switches which had failed for reasons similar to those set forth above. One type,

such as shown in Figure 1, was a surface-mounted rotary-button snap switch having a porcelain base I! supporting apair of identical stationary contacts I assembled on mounting terminals ii. The movable contact assembly it rotates in 90 steps about a central spindle under the action of a thumb button, suitable spring mechanism and releasing means, so that it snaps from the open position, shown, to a position where the movable contact assembly bridges the two stationary contacts to close a circuit. The bridging contact comprises a pair of light spring elements I! driven from the rotating mechanism and each having a widened portion at each end such as at 20. .The widened portions at either end are spaced slightly apart so that they may straddle the stationary contacts when the turn button is operated. After a period of use with tugnsten filament lamp loads of normal capacity the tips of the moving contact members were found to be burned as illustrated in Figure 1. The upper blade had one tip almost completely burned away as illustrated at 20 at the left of the figure, whereas both blades had their tips badly burned away as illustrated at 22 in the right portion of'the figure. It will be appreciated that but little life remains in this switch and that there is a possibility of it arcing-shut on any subsequent operation so that it would be impossible to open the circuit.

In Figure 2 is illustrated a somewhat different type of switch having a toggle lever 24 which moves a relatively rigid, single bridging contact between the pairs of springly stationary contacts shown at 25 and 26. Each stationary contact is formed by two springs which straddle the movable contact. However, but a single one of each has been shown, the one at 25 having a tip with two holes burned in the same as at 21, whereas the other has the leading edge badly burned away capacity snap switch an investigation was made as at 28. In the construction illustrated at 21. the inner face of the contact spring which engages the movable bridging member was so rounded that it made first engagement at the two spots which are burned through. The other one made its first engagement where the portion 28 is burned away.

The type of destruction illustrated so clearly at 21 in Figure 2 where holes are cut through the wings of the contacts is typical of the burning when the circuit is made. Undoubtedly the contacts of Figure l were cut away in just that manner by successive burning of holes. In fact, the outlines of several of them are clearly visible. Such destruction is entirely different from the damage caused by interrupting the circuit where the arcs always burn the contacts from the edge of the* wing back, never cutting holes directly through them.

Figure 3 is a replica of an oscillograph record of a circuit closing operation of a switch of the type of Figure 1 when in good condition. The record was taken, however, under most favorable conditions with only about 45 volts direct current tions dropping the current almost to zero. If the current during these oscillations resulting from relative movement between the contacts had been that excess value resulting from a tungsten filament lamp load on starting, the arcing can well be imagined and the Very detrimental effect on the contacts fully appreciated. The wavy line 33 is that produced by a 400 cycle alternating current, for the purpose of timing. It will be seen that the whole closing operation took place over approximately one cycle or in /400 of a second.

The oscillogram of Figure 4 shows the operation of the switch of Figure 2 in first breaking a circuit and again closing the same. In this case the current and voltage were approximately the same as in the first case, the steady line 34 representing the closed circuit current flowing and the sharply dropping line 35 the cessation of current as the circuit is opened to the steady no current value at 36. On closing the circuit the tremendous pulsations which took place are clearly illustrated, the current going through a number of cycles of pulsation before reaching the steady value shown at 31. Here again the 400 cycle curve 38 shows that the closing operation took almo one cycle of time.

The apparatus devised to overcome the dimculties discussed above is shown in general in Figure 5 in the form of an interchangeable switch for use three to the single gang wall box. It does not seem essential to go into details as to the construction of all of the switch mechanism more than to say that the plastic housing 40 is equipped with a neck 4| for mounting in a suitable bridge strap and that an operating handle 42 acting through a spring 43 snaps the rocker 44 from the position shown to one having the same angular displacement to the right side of a vertical plane through the rocking center 45. Mounted for movement with the rocker by being loosely positioned on the non-circular trunnion 45 and on a stud 46 extending from the rocker, is the movable contact assembly 41 shown in enlarged detail in Figures 7-10.

Each end of the molded switch housing supports a terminal plate, that at the left being numbered 48 and that at the right 49. The terminal plate 48 carries a fixed contact 50 while the terminal plate 49 carries a fixed contact 5|. As shown in front elevation in Figure 6 the edge 52 of each stationary contact, which faces toward the movable contact which engages with it when the assembly is oscillated, is tapered to a wedgelike edge. Each of the stationary contacts is a single, short, thick and relatively rigid member not subject to any substantial springing or vibrations at frequencies which would be detrimental. The supports for the stationary contacts are relatively heavy and well wedged into position in the housing.

The movable contact assembly, which is adapted to be snapped and oscillated throughout an angle of approximately 60 to open and close a circuit by bridging between stationary contacts 50 and 5|, is a multi-part structure comprising two sheet metal stampings 55 forming the contacts proper, two duplicate plates of insulation 56, and a sheet metal clamping plate 51 all stacked up as shown in Figure 8 and secured together by passing the prongs 59 and 60 struck out of the fastening plate through appropriate close-fitting openings in the sheet metal and insulation sheets and bending over the ends as at 6 l.

Each of the metal plates is stamped to provide a central disc portion 62 and a pair of angularly spaced, substantially radial arms 63 and 84, the two plates being matched so that the arms cooperate to form mating pairs. The insulation plates cover the outsides of the tightly confronting central disc portions of the sheet metal plates and extend to the arcuate outer edges 65, of substantially the same radius as the contact arms as measured from the opening, 66 which is mounted on the trunnion yoke 45. The opening 66 is of. a size to loosely fit this yoke only in the insulation plates. It is much larger in the sheet metal plates so that they are fully insulatedvfrom the trunnion. The hole 81 in the fastening plate is also much larger in order to insure clearance. It is noted that there is no fastening plate on the back, where the inner insulation plate bears against the edge of the yoke and that the turned-over ends of the fastening tabs are out of alignment with the yoke. In this way the contacts are completely insulated from the yoke and if desired, one assembly thereof can be carried by each end of the yoke for a double pole, three-way or four-way switch arrangement. The major features of novelty in the contact assembly are in the shaping and arrangement of the sheet metal punchings 55 forming the movable, spring contacts which engage the stationary contacts by straddling. The initial engagement between the contacts for each time the circuit is closed is the important period in their life and is fully protected by constructing the contacts to insure immediate and continuous engagement without vibration or chattering which might result in arcing.

The spring arms 63 and 64 which are integral with each of the central disc portions 62 so radiate therefrom that the arms cooperate in mating pairs with their inner faces in confronting relation. Near its free and each arm is flared to provide a wider spatulate tip 10 of generally triangular configuration. The central portion of the tip, forming a continuation of the main part of the arm, is first bent outwardly at H, then quickly inwardly at 12. The portion 13 just beyond the bends is substantially flat and straight, and as seen in Figure 7, is more or less rectangular. The area bordering it on the lateral edges and at the lower end is bent up out of the plane of this portion 13, giving it a dish-like configuration. The lower or outer edge 14 of the border is narrow while the side borders are wide particularly at 15, substantially in transverse alignment with the outer end of the portion 13.

The double bend ll, 12, together with the greater length of I3 than the distance between these two bends, places the very outer edge of the portion ".below the plane of the inner face ll of the main portion of the arm, as clearly seen in Figure 9, where the dotted line 18 forms the extension of the-plane of the inner face of the am. With the two arms overlying and their disc-like portions tightly clamped together, it will be seen that the respective ridge portions I6 f the opposing arms-will engage each other and be pressed tightly together by the spring action resulting from displacing each of the arms from its initial plane by the amount of the angle between 18 and the center line 19. This provides initial and mutual biasing or stressing of each of the two spring arms forming one of the movable contacts and insures that neither of these arms is permitted to act as a free cantilever spring. It cannot therefore vibrate at its natural resonant frequency and is effectively damped against any appreciable vibration by the frictional engagement of the two tips.

The flared portions 15, laterally f the parts 13, serve jointly to provide a wide funnel-like entrance for the tapered or wedge edge 52 over which the entrance takes when the movable contact engages the stationary one. o

The relatively loose, floating-mounting of the whole movable contact assembly on the snaprocker permits a self-centering action of this entrance tunnel o ver the wedge-like leading edge of the stationary contact so that when the movable contact blades beginto be wedged apart as they slide over the stationary contact, uniform pressure will be placed on both faces of the stationary contact and each spring blade will have its original stress slowly and continuously increased by virtue of the additional flexing resulting from the spreading apart of the contact blades by the wedging action of the stationary blade.

The initial stressing of the contact springs is not so great as to offer excess resistance to movement onto or off of the stationary contact so that there is no substantial slowing up of the movement imparted by the snap mechanism. The kinetic energy of the moving contact assembly is sufllcient to insure proper make" even though there is some excess pressure and the switch is provided with a positive kick-off mechanism to insure separation of the contacts even though the snap spring is insuflicient, but it has been found that contacts constructed in accordance with those just described do not have to rely on theseauxiliary aids. The main reason for this is the fact that the fold or ridge 16 existing between the lower border 14 and the substantially staight end of 13 is quite narrow and extends longitudinally in the direction of movement of the movable contacts over the stationary ones.

By having the movable contact elements mutually biased, they are prevented from acting as free springs as previously stated, so that the initial contact thereof with the stationary blade does not set the springs into violent vibration which would cause rebound. They engage over the stationary blade smoothly and with increasing pressure and the results are fully evident from the oscillograms of Figures 11 and 12 made from different sets of contacts of the same type. In Figure 11 the circuit is first broken from the fullcurrent position represented by the horizontal line ill to the no-current position 8 I, from whence it rises almost instantlyalong the substantially vertical line 82 and merges smoothly into the continuous full-current line 83 with no such violent pulsations as clearly depicted in Figures 3 and 4. The 400-cycle wave 84 shows the extremely short time necessary for closing the circuit to a continuous smooth current. It amounts to less than one-half cycle. In Figure 12 conditions are substantially the same as in Figure 11 but even less time is seen to be occupied by the full closing of the circuit. In all of the oscillograms any movement of the current line below the zero or maximum positions is due to overthrow of the galvanometer resulting from incomplete damping.

It will be seen that greatly superior results are obtained solely by the configuration of the spring blades of the movable contact and that no additional parts or complications are necessary. Furthermore, there is no increase in weight which would tend to retard the action of the snap mechanism both on make" and "break."

The features which eliminate arcing and burning 01' the contacts on "make are of no particular help on "break when, however, there is not the same arcing tendency, but nevertheless it is desirable to suppress any arcs drawn when the circuit is \broken. This is one of the functions of the skirt portions of the insulation discs. These discs are cut away as at It and as so as not to interfere with the operation of the spring contact arms, but the remaining portions have their edges so positioned that they immediately cover the stationary contacts when the movable contacts separate therefrom, and the arcs are snuii'ed out by the wiping action of the insulation discs in a manner already known.

The insulation discs have a second function of guiding the whole contact assembly so that the movable and stationary contacts are properly aligned for engagement. For this purpose they straddle both stationary contacts at all times as clearly shown in Figure 5 and are sufliciently resilient to insure proper guiding of the movable contacts onto the stationary ones.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In an electric switch of the snap type, in combination, a rigid, tapered edge, stationary contact, a movable contact for straddle cooperation therewith, a snap mechanism having an oscillatable part so associated with the second contact as to move the same toward or from the stationary contact, the second contact being free to move laterally in respect to the said part during snap movement, said movable contact comprising a pair of spring arms having tips for engagement with the stationary contact, saidarms being so shaped and attached to each other that the tips engage each other for mutual preloading of the natural spring of the arms to damp vibrations, and means t guide saidtips to the stationary contact.

2. An electric switch of the type described comprising, in combination, stationary and movable contact means, one of said means being of the rigid, single blade, tapered variety and the other comprising a pair of relatively long, light weight, spring arms fixedly mounted side-by-side for straddle engagement of the tip thereof over the first means, the spring arms being so shaped and said tips being so disposed that they normally engage each other for mutual pre-loading of the spring of the arms just sufiicient to damp such vibrations thereof which might prevent instantaneous complete closing of the circuit between the contact means, snap mechanism having a rocker, means mounting one of said contact means on said rocker with freedom of lateral movement, and means to guide the rocker mounted contact means to the stationary one.

3. An electric switch of the type described comprising, in combination, stationary and movable contact means, one of said means being of the rigid, single blade, tapered variety and the other comprising a pair of relatively long, light weight, spring arms fixedly mounted side-by-side for straddle engagement of the tips thereof over the first means, the spring arms being so shaped and said tips being so disposed that they nor,- mally engage each other for mutual pre-loading of the spring of the arms just suflicient to damp such vibrations thereof which might prevent instantaneous complete closing of the circuit between the contact means, snap mechanism having a rocker, means mounting one of said contact means on said rocker with freedom of lateral movement, and insulating guide means for the movable contact means.

4. An electric switch of the type described comprising, in combination, stationary and movable contact means, snap mechanism including an oscillatable yoke, one of said contact means being loosely mounted on said yoke for movement thereby to engage and disengage the other contact means, one of said means being of the rigid, single blade, tapered variety and the other comprising a pair of relatively long, light weight, spring arms shaped for straddle engagement over the first means, means mutually pre-loading the spring arms without increasing the weight thereof whereby they are damped against vibrations at their individual fundamental frequencies, and insulating guide means to ensure such straddle engagement.

5. In combination, a relatively stationary contact, snap mechanism including a rocker, contact means comprising a pair of bowed spring members secured together at one end and mounted loosely on said rocker for driving thereby, the free ends of said members being in close engagement with each other to stress the springs and prevent vibration at their natural periodicity upon operation of said mechanism, said engaging ends being adapted to straddle engage said stationary contact, and insulating guide means carried by said contact means and straddling said stationary contact when the same is free of the contact means to guide the latter thereover.

6. In combination, a pair of stationary contacts, snap mechanism including an oscillatable rocker, a contact assembly supported on said rocker to be moved therewith, the connection being such that the assembly is free to move laterally and tilt in-respect to the rocker, said assembly including two pairs of bowed spring members, each pair being secured together adjacent the rocker and having their free ends in close engagement with each other to stress the springs to prevent vibration thereof, said engaging ends each being adapted to straddle engage one of said stationary contacts, the free mounting on the rocker allowing proper alignment, and guide means to lead each movable contact spring pair to its stationary contact.

7. In an electric switch of the snap type, in combination, a stationary contact having a wedge-like edge, a movable contact for straddle engagement over said edge, snap mechanism having a rocker for moving said second contact toward or from the first, a floating connection between the said rocker and second contact, said movable contact comprising a pair of cooperating P spring arms substantially radiating from and connected together only near the center of oscillation of said rocker, said arms being under initial bending stress maintained by mutual engagement at the free tips, and means positioning and guiding said engaging tips in respect to said first contact to ensure simultaneous engagement of both springs with said wedge-like edge of the stationary contact.

8. In an electric switch, in combination, a rigid, stationary contact, a snap mechanism having an oscillatable rocker provided with a driving support, a movable contact assembly comprising a pair of superimposed discs of springy conducting material, means securing said discs tightly together and providing an aperture for loose sliding fit but driving connection with said support, an integral arm radiating from each disc, said arms being in confronting relationship and each having a tip for engaging with said stationary contact, said tips being each oilset toward the plane of the other arm and positioned for mutual engagement along a line extending in the direction of movement of the tips, whereby the arms are deflected apart from the tips to the discs and are under stress to prevent free vibration thereof, and an insulating sheet carried by said assembly and bearing on said stationary contact to guide said tips thereto.

MARK N. RUSSELL. SAUL KEILIEN. 

